This invention relates to an improved tire building machine and to a method of building a pneumatic tire. The machine is simple, rugged, and is capable of producing tires of excellent uniformity and quality with minimal attention of a skilled operator. The method is simple and fast.
In the building of tires having breaker plies (also referred to as "breakers" and hereafter referred to as "belts"), incorporated in the crown area of a tire, whether radial ply, bias ply, or other ply configuration, a two stage process is generally employed. During the first stage of building, a cylindrical carcass is formed having (a) one or more rubber covered cord plies wound around and interconnecting axially spaced, parallel, coaxial, bead cores, and (b) a layer of rubber sidewall stock on each sidewall of the carcass, intermediate the eventual crown area thereof and the two bead areas thereof. Such a carcass is referred to as a "first stage carcass". During the second stage of building, the shape of the first stage carcass is changed from a cylinder to a toroid and one or more rubber covered cord breaker plies and a rubber tread are added to the crown portion of the carcass to form what is referred to herein as a "green tire". The term "rubber" is used herein to describe a natural rubber, synthetic rubber and other rubbery material useful for the construction of tires. The term "cord" is used to describe single and multiple strands, filaments, wires or cables of natural and synthetic materials such as cotton, rayon, nylon, polyester, glass fiber, and the like, metal and/or such other materials as may be used as reinforcements in pneumatic tires.
In the cured, finished tire it is most important that its configuration be symmetrical about a vertical plane at right angle to the longitudinal axis of the tire. Also, the forces acting on the belts should be symmetrical and uniformly distributed while the tire is in use. Undesired displacement of the belts, and deviation of the cord angles are minimized by the herein disclosed method of building a tire, and the apparatus of this invention.
To obtain desired uniformity of a green tire, it is known to bond a plurality of belts to one and another on another molding drum to form a cylindrical composite belt in advance, and then, to bond the composite belt to the outer periphery of a green first stage carcass. An apparatus for forming such composite belts is disclosed in U.S. Pat. No. 3,441,074.
It is also well known to press or "print" a belt or tread on to a green carcass. However, when a belt was pressed on to the carcass, the carcass was either (a) supported above the beads with (i) an inflatable bladder support, or (ii) with a rigid support member; or, (b) there was no control of the printing location where the belt was applied radially relative to the longitudinal axis of the first stage carcass.
One of the most preferred prior art methods of applying belts to a first stage carcass is with a machine using movable shaping rings (referred to as "belt rings") which attempt to control both the outer circumference of the carcass, and, the distance from the longitudinal axis at which the belt is to be placed. The belt rings confine the carcass, providing a slight (about 0.0625") bulge of the median circumferential (crown) portion of the the carcass on which the belts are then positioned. Such a machine is disclosed in South African patent application No. 721,237, inter alia.
Where a tread was rolled on to a belted carcass, as for example when retreading a tire as disclosed in U.S. Pat. No. 3,989,563, no effort was made to provide a fixed radial distance of the point of adhesion of the tread relative to the longitudinal axis of the tire, and no thought was given to positioning the belts in this manner.
Undeniably effective as the belt ring machine is in the mass production of high quality tires, there are certain problems with respect to its utilization which have defied economically viable solutions. In particular, the complicated mechanism of the belt ring machine inevitably requires high maintenance with concomitantly high down-time and costs. Moreover, it is necessary to carry a high inventory of expensive machine components because they are prone to damage during use. Still other less desirable features of the belt ring machine is that it occupies a relatively large space on the floor of a tire plant, and, requires a level of due care for its operation not readily accorded the machine in day to day production. Most of all, there has been an as yet unfulfilled need for an uncomplicated machine which will match or better the performance of a belt ring machine, reliably and economically, with a minimum of highly skilled attention. The instant invention provides such a machine, and a simple method for its operation.